1. Field of the Invention
The present invention relates generally to improved energy efficient air and process gas adsorption/desorption vessel assemblies with removable radial-flow adsorption bed cartridge subassemblies, particularly applied to VSA gas separation vessels producing a high purity oxygen gas product or other purified process product.
Within the process gas industry, and in particular within the air separation market, the continuing increasing costs of electric power makes the energy efficiency of gas separation systems of ever increasing importance. The common art methods of separating a desired molecular gas from a mixture of process gases, or the separation of nitrogen from air to provide a highly predominant oxygen gaseous product stream, commonly includes the utilization of (a) power-intensive multi-stage membrane separation system, or refrigerated or cryogenic generated liquid extraction systems; (b) pressure swing adsorption (PSA) systems for producing moderate pressure supplies of predominant oxygen gas; and (c) vacuum pressure swing adsorption (VPSA) units, or also interchangeably referred to as vacuum swing adsorption swing units (VSA) units. VSA units generally require the least of all system power consumptions per ton of product gas of less than 100% purity.
Controlled temperature swing adsorption (TSA) applied within PSA or VSA cycles can be employed when a selected preferred adsorbent exhibits superior gas adsorption/desorption performance within specific ranges of operating gas temperature. Application of TSA is typically employed in the example separation of hydrogen from within a catalytic steam-reforming process reaction system that produces a typical process gas stream mixture of hydrogen, carbon monoxide and carbon dioxide, and the separation of one or more hydrocarbon gases from a petrochemical or petroleum refining process supplied feed gas mixture of hydrocarbon gases. In the case of adsorbed hydrogen being the preferred gas product, the hydrogen gas product is discharged from the gas separation vessel during the desorption cycle portion of the gas separation process.
There is therefore a need for a gas separation vessel apparatus assembly that can operate with, but not limited to, low pressure gas feedstock adsorption/desorption systems with extraordinary low system differential pressures that further contributes to achieving the lowest VSA gas separation systems energy consumptions (or Best Available Technology energy performance). A need also exists for an assembly that addresses other important long-term operational requirement needs for future rapid adsorbent replacement for upgraded performance capabilities.
Gas separation feedstock gases can comprise low positive pressure ‘vapor recovery’ or process ‘off-gases’ developed within facility petrochemical process or petroleum refining operations. They can also comprise feedstock air (or conditioned air at atmospheric or slight sub-atmospheric pressure) to produce a predominant rich oxygen product gas of lesser flow during a gas separation vessel's adsorption sequence of operation, and a predominant nitrogen gas waste gas of greater flow during a gas separation vessel desorption sequence of operation.
In the case of petroleum refining operations wherein at least two hydrocarbon gases having different adsorption characteristics are present, the more strongly adsorbable gas can be an impurity which is removed from the less strongly adsorbable gas which is taken off as a product gas; or, the more strongly adsorbable gas can be the desired product gas that is separated from the less strongly adsorbable gas. A petroleum refining process stream mixture of propylene and propane is such an example. Propylene is the more valued product and the more strongly adsorbable gas which can be separated from the less strongly adsorbable propane gas of lesser value.
In the case with large industrial petrochemical and petroleum refining facilities, process gas streams may be varied in composition within a relative short time period, compared to other industries continuous process streams that may remain unchanged for a number of years. From a facility lost revenue and operating cost standpoint, it is important to be able to minimize labor, material expense, and the time required to remove and replace the old adsorbents with new optimum performance adsorption materials as required to adapt existing gas separation or adsorption-desorption vessels to these new variances in process gas composition streams. Especially in low pressure gas streams, unnecessarily high adsorbent bed gas velocities and accompanying separation vessel pressure drops can result in the loss of adsorbent performance from bed fluidization and significant increased electric power costs for gas compression. To achieve the combined needs of providing operating high energy efficient gas separation vessels that are economically adaptable to rapid upgrades or changes in adsorbent bed material, the present invention includes an improved gas separation vessel assembly and internal subassembly device Adapted to satisfy these needs.
2. Description of Related Art
A sample review of known U.S. patents having variations of typical current art gas separation vessels within PSA and VSA systems includes the following: U.S. Pat. No. 5,759,242 discloses the design of a vertical adsorber vessel having an internal means to direct gas flows radially through the molecular sieve adsorbent material contained within the welded-closed vertical adsorber vessel. The ‘Background of the Art’ within U.S. Pat. No. 5,759,242 extensively describes the numerous operating shortcomings of conventional VSA vertical adsorber vessels having axial gas flows through the vertical beds of molecular sieve adsorbents.
U.S. Pat. No. 5,964,259 discloses an apparatus design and method of loading multiple molecular sieve adsorbents into the interior of a welded-closed vertical adsorber vessel therein designed to contain vertical radial-flow adsorbent beds as described in U.S. Pat. No. 5,759,242.
U.S. Pat. No. 6,086,659 addresses adsorption vessel design approaches relating to radial-flow type vessels employing temperature swing adsorption (“TSA”), in order to minimize or offset the multiple consequences of cyclic thermal expansion and contraction of materials within the adsorption vessel. The U.S. Pat. No. 6,086,659 discloses a welded-closed type vertical adsorption vessel, therein containing multiple radially gas-outward flow vertical beds concentrically-positioned around the vessel center axis positioned cylindrical feed gas delivery chamber into which feed gas is introduced through the top of the vessel. Each described vertical adsorbent bed can contain a different adsorbent material, the containment of each bed being accomplished with the invention described perforated metal bed partition and screen design configuration to withstand thermal expansion and contraction stresses. The final product gas exits the outer-most concentric bed retention screen into the outer annulus gas flow space between the vessel inside diameter and the described outer concentric bed retention screen. The product gas is thereafter withdrawn through the bottom portion of the vessel assembly apparatus. Individual single flanged nozzles are provided and aligned-positioned in the top welded head of the vessel, to enable the filling or empting of each separate individual adsorbent bed. U.S. Pat. No. 6,770,120 discloses a welded-closed type vertical adsorption vessel, therein containing either (1) two radial gas-inward flow connected vertical beds concentrically-positioned around the vessel center axis positioned inner cylindrical product delivery chamber through which the product gas exits from the bottom of the vessel; (2) one radial gas-inward flow connected vertical bed concentrically-positioned around the vessel center axis positioned inner cylindrical volume space that is occupied by a vertical axial-flow adsorption bed receiving a series-connected flow of gases from the upstream radial-flow adsorption bed, with final product gas flow exiting from the bottom of the vertical vessel; or (3) one radial gas-inward flow connected vertical bed concentrically-positioned around the vertical vessel center axis positioned inner cylindrical volume space that can be utilized in one variation as a gas storage tank. U.S. Pat. Nos. 5,674,311, 5,538,544, and 6,334,889 respectively describe methods by which the conventional art PSA and VSA systems' (comprising vertical adsorber vessels and vertically deep adsorbent beds) inherit problems of adsorbent bed temperature gradients, uneven gas flow distribution, and adsorbent bed fluidization can be reduced to improve adsorbent bed efficiencies.
Those skilled in the art will appreciate that the various approaches to PSA and VSA vessel apparatus separation of gases, contained within the above example patents and other existing published art, predominantly limit themselves to employed vertical vessel apparatus that comprise either vertical axial gas flows or horizontal radial gas flows of gases through a ‘fixed’ vertically disposed bed column of adsorbent material. The described current art vertical vessel configurations share many common limitations that negatively impact the vessel's overall consistent gas product purity, maintenance of operating adsorbent bed uniformity and adsorbent structural form integrity, and economical power consumption. Previous art vessels have not addressed the need for a means to carry out a rapid and economical adsorbent bed removal and replacement as new improved performance adsorbent materials become available, or when the existing adsorbent bed becomes contaminated from a process upstream upset condition that contaminates both the process feed gas supplied to the gas separation vessels and the adsorbent materials contained therein.
A need exists, therefore, for a horizontal vessel apparatus that can overcome conventional art air or process gas separation vessel apparatus limitations. A need also exists for a vertical vessel apparatus that can overcome conventional art air or process gas separation vessel apparatus limitations. The presented invention gas separation vessel apparatus, and embodiments thereof, satisfy these needs and have the following objectives:                1. It is a first objective to significantly reduce the electric power consumption by reducing the air or process gas separation vessel's radial-gas flow adsorbent bed depth, and therefore reduce the gas flow differential pressure across the gas flow bed depth that conventionally requires gas compression power to overcome.        2. It is a second objective to provide an air or process gas separation vessel apparatus that greatly reduces the molecular sieve bed gas velocities as are employed within conventional PSA and VSA axial gas flow vertical vessel systems, and further reduce current art radial-gas flow bed velocities, thereby achieving significantly increased feedstock gases ‘residence time’ for gases to permeate into the porous structure of employed molecular sieve adsorbent bed material and decreased potential of “bed fluidization” with accompanying molecular sieve material degrading attrition from occurring.        3. It is a third objective to achieve a level of precise quantitative adsorbent placement and desired compaction within each multiple separated adsorbent bed material segments that make up the total employed adsorbent bed material employed with each invention embodied radial-flow bed cartridge subassembly. This degree of adsorption bed placement quality control is not possible with existing art axial flow or radial flow adsorbent beds contained within present art vertical gas separation vessels. This objective can also improve both the uniform adsorbent material's adsorption-desorption performance throughout the invention embodied radial-flow bed cartridge, as well as to further eliminate the potential of “bed fluidization” described in the above second objective.        4. It is a fourth objective to provide the means of eliminating conventional PSA or VSA air separation vertical vessel's deep molecular sieve adsorbent beds' operational axial gas flow temperature variance characteristics that can negatively affect the beds' nitrogen adsorbed gas separation efficiencies.        5. It is a fifth objective of the present air or process gas separation vessel apparatus described herein, to provide an apparatus can be adaptable to a manufacturer's or system fabricator's chosen selection of adsorbent molecular sieve materials, desired product gas production rate and purity, length and diameter dimensional configurations of vessel assemblies, and the employment of selected embodiments and variations provided by the invention.        6. It is a sixth objective that the employed air or process gas separation vessel apparatus have the inherit subassembly design means that can accommodate the long-term operational employment of both present or later added future molecular sieve material adsorbents whose fragile structures can be incompatible with the combined cyclic adsorption-desorption pressure swings and weight bearing loads imposed by conventional vertical adsorber vessel designs having either radial or axial style gas flows through their common configuration of vertically disposed and fixed adsorbent beds.        
All references cited herein are incorporated by reference to the maximum extent allowable by law. To the extent a reference may not be fully incorporated herein, it is incorporated by reference for background purposes and indicative of the knowledge of one of ordinary skill in the art.